The .lib is not included in your project. Make sure you are linking it in;
Configuration Properties -> Linker -> Input -> Additional Dependencies

Another altnerative is to simply copy the .lib to your project folder but don't, it's bound to create problems later on.

Sometimes the .lib is not shipped with the library, so you need to compile it yourself.
The README will tell you this. If this is the case, they usually ship with a .sln file you can open and the just compile it into a .lib file which you then reference in your main application, as I wrote above